1. Field of the Invention
The present invention relates to a wrist of a robot, and in particular to laying structure of lines such as cables and pipes for supplying electric power and fluid such as air and water or discharging fluid to or from an end effector such as a hand and a tool to be attached to the wrist of the robot.
2. Description of Related Art
An end effector such as a hand and a gun as a tool is attached to a wrist of a robot provided at a distal end of an arm for carrying out various operations. Lines of cables/pipes for flowing air, liquid such as water and electricity to the end effector for an operation thereof are arranged through the arm. Since the arm and wrist of the robot perform complex motions, the lines may interfere with other components or peripheral equipments of the robot to lower durability of the lines. There is known a technique of laying lines of cables/pipes inside the wrist or arm of the robot from Japanese Patent Publication No. 2000-334689 and Japanese Patent Publication No. Hei-10-329079. Further, a technique of arranging guiding means for guiding the lines of cables/pipes is known from Japanese Patent Publication No. 2001-150382.
Irrespective of laying location of the lines inside or outside of the arm or wrist of the robot, the lines are subjected to bending, twisting and translation with the complex motion of the arm and wrist of the robot.
In general, the wrist of the robot has three joints for allowing three degrees of freedom around three different axes. Each of the joints is provided with a wrist element rotatable around one of the three axes independently of the other axes. Therefore, when a first wrist element as a base of the wrist with respect to the arm is rotated around the first axis, for instance, the second and third wrist elements connected to the first wrist element and also the end effector attached to the third wrist element are rotated, to cause bending, twisting and translation of the lines entirely from the arm to the end effector. Similarly, when the second wrist element or the third wrist element is rotated, the lines are influenced by the rotation of the wrist element.
Thus, the entire lines of cables/pipes through the arm to the end effector are influenced by rotations of the respective wrist elements at the joints to make bending, twisting and translation.
Further, when the three wrist elements are rotated simultaneously around the respective axes, a specific section of the lines is subjected to a complex motion of bending, twisting and translation by the complex motion of the three wrist elements to make it difficult to obtain a predetermined durability of the lines. Also, there is a problem of restriction of angle of rotation of the wrist element in dependence of angular positions of the other wrist elements.